I have searched around and do not have surplus NVMe drives. I have lots of surplus SATA and SAS drives. I am still experimenting to see what might be the cause. I’ve ruled out heat and system load completely now. The issue happens after extended high IO to or from the NVMe. It seems that the command queue of the NVMe might be being exceeded. I’ve not been able to prove this. Maybe over this weekend I can put more time into it.